Please post a copy of a chkdsk report on your C partition select Start, Run, type "cmd" without quotes in the box and press the ENTER key. Type chkdsk and press the ENTER key and a report, detailing amongst other things a summary of how the disk space is utilised, is provided. If you want a report on a partition or drive other than C you need to go to that partition. To access F, where F is the required partition you type F: and press the ENTER key.
Copying reports from a command prompt can be tricky. Right click and select Mark. This enables you to highlight selected text and click to copy. You then go to an open Word, Notepad or similar file, right click and paste. The selected text transfers from your clipboard to the open file. You can paste directly into a reply message to most forums.
In Windows 7 you may need to use an Elevated Command Prompt;
http://www.sevenforums.com/tutorials/783-elevated-command-prompt.html
Would you also run the Windows 7 Memory Diagnostic Tool:
http://www.sevenforums.com/tutorials/715-memory-diagnostics-tool.html